Music collection navigation device and method

ABSTRACT

An audio navigation device comprising an input means for inputting two or more audio pieces into the navigation device; a spatialization means for allocating a position in the form of a unique spatial coordinate to each audio piece and arranging the audio pieces in a multi-dimensional arrangement; a generating means for generating a binaural audio output for each audio piece, wherein the audio output simulates sounds that would be made by one or more physical sources located at the given position of each audio piece; an output means for simultaneously outputting multiple audio pieces as binaural audio output to a user; a navigation means for enabling a user to navigate around the audio outputs in the multi-dimensional arrangement; and a selection means for allowing a user to select a single audio output.

RELATED APPLICATIONS

The application is a continuation of, and claims priority to each of,U.S. patent application Ser. No. 16/937,152, filed Jul. 23, 2020, andentitled “MUSIC COLLECTION NAVIGATION DEVICE AND METHOD,” which is acontinuation of U.S. patent application Ser. No. 16/405,983 now U.S.Pat. No. 10,764,706), filed May 7, 2019, and entitled “MUSIC COLLECTIONNAVIGATION DEVICE AND METHOD,” which is a continuation of U.S. patentapplication Ser. No. 15/135,284 (now U.S. Pat. No. 10,334,385), filedApr. 21, 2016, and entitled “MUSIC COLLECTION NAVIGATION DEVICE ANDMETHOD,” which is a continuation of U.S. patent application Ser. No.14/719,775 (now U.S. Pat. No. 9,363,619), filed May 22, 2015, andentitled “MUSIC COLLECTION NAVIGATION DEVICE AND METHOD,” which is acontinuation of U.S. patent application Ser. No. 13/060,090 (now U.S.Pat. No. 9,043,005), filed May 12, 2011, and entitled “MUSIC COLLECTIONNAVIGATION DEVICE AND METHOD,” which is a national stage of PCTInternational Application No. PCT/GB2009/002042, filed on Aug. 20, 2009,published on Feb. 25, 2010 as WO 2010/020788, and entitled “MUSICCOLLECTION NAVIGATION DEVICE AND METHOD,” each of which applicationsclaims further priority to GB Application No. 0815362.9, filed Aug. 22,2008. The foregoing applications are hereby incorporated by referenceherein in their respective entireties.

TECHNICAL FIELD

The present application relates generally to a music collectionnavigation device and method and more specifically a spatial audiointerface, which allows a user to explore a music collection arranged ina two or three dimensional space.

BACKGROUND

The most common interface for accessing a music collection is atext-based list. Music collection navigation is used in personal musicsystems and also in online music stores. For example, the iTunes digitalmusic collection allows a user to search for an explicitly chosen songname, album name or artist name. A list of potential matches isreturned, usually in the form of a list and often ranked in terms ofrelevance. This requires a user to know in advance the details of themusic they are looking for, which inhibits a user from discovering newmusic. The user is often given a list of several thousand songs fromwhich to choose and, because a user is only able to listen to a singlesong at any one time, they need to invest a significant amount of timeto listen to, and browse through, the choices offered, to make adecision about to which song to listen.

Previous audio interfaces have focused on spatializing the soundssources and approaches to overcome errors introduced in thispresentation of the sounds. In known interfaces, sound sources arepresented in a virtual position in front of the listener to aidlocalization and decrease problems introduced in interpolating thehead-related transfer functions. The AudioStreamer interface developedin the 1990s presented a user with three simultaneously playing soundssources, primarily recording of news radio programs. The sounds werespatially panned to static locations directly in front and at sixtydegrees to either side of the listener. The virtual position of thesound sources was calculated using head-related transfer functions(HRTFs). Sensors positioned around the listener allowed the sound sourcepreferred by a user to be tracked without any further user input.

Several audio-only interfaces have also been developed to assist a userin re-mixing multiple tracks of the same song, such as the Music Scopeheadphones interface developed by Hamanaka and Lee. Sensors on theheadphones were used to track a user's movement but the invention failedto ensure the accurate spatialization of the sounds because it isconcerned with re-mixing rather than navigating through multiple songs.Without accurate spatialization of the sounds sources, a listener islikely to be confused and any selection of sounds source by the user isdifficult and so inaccurate. These existing interfaces do not allow auser to directly interact with the sound sources to select which optionto play. By using fixed sounds sources, such interfaces are unsuitablefor exploring a large music collection.

It is also known to create a combined visual and audio interface whereinmusic is spatialized for a loudspeaker setup, such as the Islands ofMusic interface developed by Knees et al. However, such a system wouldnot be suitable for headphone listening and so cannot be applied, forexample, to a personal music system or to mobile phone applications.

The majority of existing audio interfaces for interaction with audiofiles use non-individualized HRTFs to spatialize the sound source andare concerned with overcoming errors common to such methods. Theinterfaces presented to a user are limited to a front position withrespect to a user to aid localization. The systems are kept static todecrease computational load. None of the known interfaces disclose anaccurate method for presenting the spatial audio with which a user isallowed to interact. The placement of the sounds in the virtualenvironment is key factor in allowing a user to interact with multiplesources simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the subject disclosureare described with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 is a plan view of a remote controller constructed in accordancewith the present application;

FIG. 2 is a schematic view of the spatialization and selection steps ofthe method of the present application;

FIG. 3 is a schematic view to show how the remote controller is used toselect songs in front and behind a user in accordance with the presentapplication;

FIG. 4 is an illustration of how the zoom function of the remotecontroller of the present application can be used to navigate throughdense or sparse data;

FIGS. 5A and 5B are flow diagrams illustrating the Ambisonics encodingand decoding according to the present application;

FIG. 6 is a schematic plan view of the possible symmetric virtualloudspeaker configurations for four, six and eight loudspeakers,discussed in respect of the testing of the present application;

FIGS. 7A, 7B, 7C, 7D, and 7E show graphs illustrating the ITD forvarious frequencies;

FIGS. 8A, 8B, and 8C show graphs illustrating the error in dB overfrequency for the contralateral ear;

FIGS. 9A, 9B, and 9C show graphs illustrating the error in dB overfrequency for the ipsilateral ear;

FIG. 10A shows a graph illustrating the Euclidean distance for thecontralateral and the ipsilateral ears for the on-axis (circles) andoff-axis (triangles); and

FIG. 10B shows a graph illustrating the Euclidean distance for thecontralateral and the ipsilateral ears for first (circles), second(triangles) and third (squares) orders.

DETAILED DESCRIPTION

The present application sets out to provide an improved method andapparatus for music collection navigation, which alleviates the problemsdescribed above by providing a method and apparatus which allows a userto make a quicker a more informed decision about which piece of music towhich to listen.

Accordingly, in a first aspect the present embodiments provide an audionavigation device comprising:

an input means for inputting two or more audio pieces into thenavigation device;

a spatialization means for allocating a position in the form of a uniquespatial coordinate to each audio piece and arranging the audio pieces ina multi-dimensional arrangement;

a generating means for generating a binaural audio output for each audiopiece, wherein the audio output simulates sounds that would be made byone or more physical sources located at the given position of each audiopiece;

an output means for simultaneously outputting multiple audio pieces asbinaural audio output to a user;

a navigation means for enabling a user to navigate around the audiooutputs in the multi-dimensional arrangement;

a selection means for allowing a user to select a single audio output.

Within the context of this specification the word “comprises” is takento mean “includes, among other things”. It is not intended to beconstrued as “consists of only”. The term “spatialization” is understoodto refer to localization or placement of sounds in a virtual space,which creates an illusion whereby the origin of the sound appears to belocated in a specific physical position.

By presenting audio pieces or songs in a two or three dimensional spacearound a user's head, a user is able to judge several piecessimultaneously without the need for the user to know in advance thepiece or song that they are searching for. The present embodiments canalso scale to use with large music collections and does not rely onvisual feedback or require a user to read textual metadata, such asartist and album. This makes the present embodiments beneficial to userswho cannot see, but also allows those that can see to perform the audiosearching task in addition to other tasks requiring sight. A user isable to better interact with the songs and have more flexible playbackoptions when choosing which song to play. The present embodimentsprovide a quicker, more accurate and more direct display of the musicwithout the need to rely on a text based list.

Preferably, the generating means generates a binaural audio output usingAmbisonics encoding and decoding.

More preferably, the generating means generates a binaural audio outputusing first order Ambisonics encoding and decoding.

By using Ambisonics encoding and decoding a constant number of HRTFs arerequired independent of the number of sound sources, which are convolvedwithout any need for interpolation. This reduces the computationalcomplexity of the present embodiments, which is particularly pertinentwhen the present embodiments are used to navigate through large musiccollections. That is, the only limits on the number of sounds sourcesthat are simultaneously played around a listener are psychoacousticalrather than any limitations imposed by the use of HRTFs. First orderAmbisonics was surprisingly shown to be the most accurate method forsynthesizing a binaural output. First order Ambisonics also reduces thecomputational load.

Preferably, the generating means generates a binaural audio outputwherein the audio output simulates sounds that would be generated bymultiple sources.

Preferably, the input means is adapted to automatically input audiopieces according to a preference input by the user.

The present embodiments can adapt the audio output for a user dependingon a user's likes and dislikes. For example a “seed song”, which theuser typically likes, can be used to generate a list of songs for a userto navigate through. This method is much quicker than conventionalkeyword searching, where a user has to open each recommended audio pieceindividually to narrow their selection.

Preferably, the output means comprise a pair of headphones.

By using headphones, the present embodiments can be used with personalmusic players and other mobile devices such as mobile phones.

Optionally, the output means comprise a pair of loudspeakers.

By using loudspeakers, the present embodiments can be used in arecording studio in professional audio navigation applications. It is tobe understood that, in an alternative embodiment of the presentapplication, the generating means generates an audio output, which issuitable for loudspeakers and is not binaural. Multiple loudspeakers areused as an output means for simultaneously outputting multiple audiopieces.

Preferably, the navigation means comprises a remote controller, such asa keyboard, a joystick, a touch screen device, one or moreaccelerometers, or video motion tracking.

More preferably, the navigation means is adapted to include a zoomfunction.

A zoom function allows a user to easily select the number of audiopieces that are output at any one time and reach a comfortable levelaccording to personal preference.

Preferably, the spatialization means is adapted to arrange each audiooutput according to its content.

The user can choose to be presented with audio output that is similar incontent, for example the output can be grouped according to theemotional content of the audio pieces. This can be done according totags associated with each audio piece.

Optionally, the navigation device further comprises a play listgenerator or a mapping means for storing predetermined similarity maps.

Mapping audio pieces according to similarity can encourage a user tolisten to new music and can also make navigation through a large musiccollection easier and more efficient.

Preferably, the output means is adapted to play about four audio piecessimultaneously.

It has been found that four audio pieces allows for efficientpresentation of the audio pieces without causing confusion to a user.

Preferably, the spatialization means arranges each audio output in a twodimensional space.

Optionally, the spatialization means arranges each audio output in athree dimensional space.

Preferably, the spatialization means arranges each audio output in an“on-axis” configuration wherein the audio output simulates sounds thatwould be made by physical sources located directly in front and directlybehind a user's head.

Preferably, the spatialization means arranges each audio output in anon-axis configuration at ninety degree intervals.

An “on-axis configuration” is understood to mean that the virtualloudspeakers are located directly to the front and back of thelistener's head. For first order decoding further speakers are locateddirectly to the left and the right of a user's head. An on-axisconfiguration has been shown to be the best configuration for binauralaudio output.

Optionally, the spatialization means arranges each audio output in anon-axis configuration at sixty degree intervals.

Optionally, the spatialization means arranges each audio output in anon-axis configuration at 22.5 degree intervals.

Preferably, each audio piece is any one or more of a song, an audiostream, speech or a sound effect.

Optionally, the music navigation device further comprises a visualdisplay means.

In a second aspect, the present embodiments provide a music navigationmethod comprising the following steps:

inputting two or more audio pieces into the navigation device;

allocating a position in the form of a unique spatial coordinate to eachaudio piece;

arranging the audio piece in a multi-dimensional arrangement;

generating a binaural audio output for each audio piece, wherein theaudio output simulates sounds that would be made by one or more physicalsources located at the given position of each audio piece;

simultaneously outputting multiple audio pieces as binaural audio outputto a user;

navigating around the audio outputs in the multi-dimensionalarrangement; and

selecting a single audio output.

For the purposes of clarity and a concise description, features aredescribed herein as part of the same or separate embodiments; however itwill be appreciated that the scope of the various embodiments mayinclude ones having combinations of all or some of the featuresdescribed.

The present embodiments can use virtual Ambisonics to convert anAmbisonics B-format sound field into a binaural signal to be outputthrough the headphones to a user. As shown in FIGS. 5A and 5B, thesystem encodes the sound sources into Ambisonics B-format and thendecodes the B-format into speaker signals before convolving with headrelated transfer functions (HRTFs) to render signals for playback overheadphones. First order Ambisonics has been found advantageous for thismethod and lower order encoding and decoding can be used to decrease thecomputational load. First order decoding has been shown to providesufficient spatialization accuracy for the purposes of the presentembodiments. However, any order of Ambisonics can be used. The hereindescription of the embodiments refers to first to third order Ambisonicsbut any order can be used by applying the appropriate algorithms Usingthe method of the present embodiments, a constant number of HRTFs areused independent of the number of sound sources convolved and does notdepend on interpolation or a dense measurement set. The sound field isencoded in B-format, which simplifies the calculations to rotate thesound field, as would occur if the listener turned their head.

The collection of music is arranged according to any suitable algorithmfor assigning unique spatial coordinates to each song in a collection.Thus, each song is arranged in a virtual space according to the songsperceived distance from the user and also the angle of the song inrelation to the user. The coordinates can be assigned in many ways. Forexample, the songs can be arranged according to properties of the songsor randomly.

The coordinates can be points on a circle or a sphere or any two orthree dimensional object with the virtual acoustic space. The soundssources presented are not limited to music but can be any audio stream,such as speech or sound effects.

A hand-held remote controller 1 is provided to navigate through thesongs and allows a user to select a song to listen to in full stereo. Asshown in FIG. 1 , the controller 1 allows a user to switch betweencollections. Button A allows a user to select the song he wishes tolisten to in full and button B is depressed to change the type of songs,i.e., the collection, which is arranged around the user's head. It isenvisaged that the present embodiments can be used in conjunction withany play list generator or similarity map to allow the song collectionto be arranged around a user according to a user's tastes. For example,the songs presented to the user can be selected from a “seed” song,which a user typically likes. The remote controller shown comprisesthree accelerometers, seven buttons and four further buttons arranged ina cross formation, four LEDs. The remote controller is able to vibrate.

As shown in FIG. 2 , in use, a user 5 points the remote controller 1towards the song positioned in virtual space that he wishes to selectand moves the controller towards the song he is interested in. The usercan choose to interpret the interface from one of two equivalentviewpoints. If the user perceives himself to be static and the songs tobe moving around him then they point the remote controller at the songto bring the song towards them. If a user perceives himself to be mobileand moving around between the songs, with the songs in a fixed position,then they point the controller in the direction in which they would liketo move. From either viewpoint the user is able to resolve anyfront-back confusion and other localization problems by moving in theenvironment and adjusting accordingly.

The accelerometers within the remote controller 1 use Bluetooth tocommunicate with the processing unit/computer. There is no absolutedirection in which the remote controller 1 needs to be pointed. The usercan be facing towards or away from the computer and it has no effect onthe direction of movement within the interface. The position of theremote controller 1 is controlled with respect to the headphones. Thedata from the accelerometers is processed to extract the generaldirection that the remote controller 1 is pointing in three dimensions.The user depresses button B to indicate when movement is intentional andmoves with constant velocity in the desired direction. As shown in FIG.3 , a user 5 is able to access songs 3 in front of him when the remotecontroller 1 is facing upwards, that is with the A button uppermost. Toaccess songs behind him, he can reach over his shoulder with the remotecontroller 1, such that the controller 1 is facing downwards, with the Abutton lowermost. The remote controller 1 vibrates when the user isclose enough to the song to select the song using button A. The userthen depresses button A to listen to the song in stereo. When a user hasfinished listening to the song, they can depress button A again toreturn to the two/three dimensional spatial arrangement of songs. Theywill again hear multiple songs playing simultaneously and continuouslyaround their head and use the remote controller 1 to navigate around thespace before selecting another song, as described above.

When a song is selected, it can also be used for further processing,such as automatically generating a recommended play list or purchasingthe song from an online music store.

As shown in FIG. 4 , when navigating through the audio space, the useris also able to use the remote controller 1 to zoom in and out to hearmore songs or fewer songs. This allows a user to balance the number ofsongs 3 to which he listens. If the data is too clustered around a userso that a large number of songs are playing at once, then the user canzoom out and listen to fewer songs. If the data is too sparse and theuser feels lost because he cannot find a song to which to listen, thenhe can zoom in and increase the number of songs playing at that time.The zoom function increases or decreases the listening area. As shown inFIG. 4 , if the songs are arrange in a circle surrounding the user, whenthe user presses the [+] button to zoom in the radius of the circleshrinks allowing only the closest songs to be heard. When the userpresses the [−] button the radius of the circle increases allowing moresongs to be heard.

It is possible for an alternative controller to be used with the presentembodiments and for alternative functions to be provided. The arrow keysof a conventional keyboard, a joystick or the touch screen functions ofan iPhone can be used to control the apparatus. For example, a furtherfunction can allow a user can select the type of listening environmentin which the sound sources should be played, such as a living room or acathedral. Although not described in the above-referenced example, it isalso envisaged that a visual display could be provided. Although thesystem is primarily audio based if the user wished to learn furtherdetails about the songs that are selected then a visual display or atext-to speech function could be used to provide the requiredinformation.

Spatial Audio

The present embodiments can use virtual Ambisonics to convert anAmbisonics B-format sound field into a binaural signal to be outputthrough the headphones to a user. As shown in FIGS. Sa and Sb, thesystem encodes the sound sources into Ambisonics B-format and thendecodes the B-format into speaker signals before convolving with headrelated transfer functions (HRTFs) to render signals for playback overheadphones. First order Ambisonics has been found advantageous for thismethod and lower order encoding and decoding can be used to decrease thecomputational load. First order decoding has been shown to providesufficient spatialization accuracy for the purposes of the presentembodiments. However, any order of Ambisonics can be used. The hereindescription of the embodiments refers to first to third order Ambisonicsbut any order can be used by applying the appropriate algorithms Usingthe method of the present embodiments, a constant number of HRTFs areused independent of the number of sound sources convolved and does notdepend on interpolation or a dense measurement set. The sound field isencoded in B-format, which simplifies the calculations to rotate thesound field, as would occur if the listener turned their head.

The HRTFs of the present embodiments are used to filter the audiosignals to simulate the sounds that would be made by a physical sourcelocated at a given position with respect to a listener. This isdistinctly different from traditional stereo headphone listening wherethe sounds appear to be originating between a listener's ears, insidetheir head. However, the HRTFs are only approximations of a user'spersonal HRTFs and it is understood that errors can occur. For example,a sound source can appear as if it is located behind the listener whenit should appear to be located in front of the listener. The presentembodiments overcomes these errors by enabling a user to manually changethe sound field, simulating moving their head.

Ambisonics is applied to the present embodiments to optimize thebinaural rendering of sounds over headphones. The method considers thelistener's head to be kept in an ideal spot and allows the “virtualloudspeakers” to be moved around the listener and be placed anywhere.The method uses horizontal-only Ambisonics. We can assume that novertical information needs to be considered because the elevation of anysource will always be equal to zero. However, it is to be understoodthat the method could also be extended to include height information.The examples given below refer to first to third order Ambisonics.However, the method could be extended to higher orders.

The method of the present embodiments requires at least three B-formatchannels of audio as an input signal, which are mixed down to output twochannels. The HRTF pair is found for each B-format channel. Thus, atfirst order, three pairs of HRTFs (six filters) are required for anyloudspeaker arrangement. Equations 1 show how the HRTF for each B-formatchannel is computed from the chosen virtual loudspeaker layout.Equations 1 is derived from the Furse-Malham coefficients forhorizontal-only Ambisonics:

$\begin{matrix}{{W^{hrtf} = {1/\sqrt{2x{\sum\limits_{k = 1}^{N}\left( {S\frac{hrtf}{k}} \right)}}}}{W^{hrtf} = {\sum\limits_{k = 1}^{N}\left( {{\cos\left( 0_{k} \right)}xS_{k}^{hrtf}} \right)}}{Y^{hrtf} = {\sum\limits_{k = 1}^{N}\left( {{\sin\left( 0_{k} \right)}xS_{k}^{hrtf}} \right)}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

N is the number of virtual loudspeakers each with a correspondingazimuth θ and HRTF, S^(hrtf)

Equation 2 describes how the signals for each ear are then calculated:Left=(W⊗W _(L) ^(hrtf))+(X⊗X _(L) ^(hrft))+(Y⊗Y _(L) ^(hrtf))Right=(W⊗W _(R) ^(hrtf))+(X⊗X _(R) ^(hrtf))+(Y⊗Y _(R) ^(hrtf))  Equation2

It has been found that for the best results and the optimum decoding,Ambisonics should be decoded to regular loudspeaker distributions. Thevirtual loudspeakers are distributed about the listener so that the leftand rights sides are symmetric. The left and right HRTFs of theomni-directional channel W are the same as are the left and right HRTFsof the X channel, which captures front and back information. The leftand right HRTFs are equal but phase inverted. Thus, only threeindividual HRTFs, not pairs of HRTFs, are needed for a horizontalbinaural rendering, as shown in Equation 3:Left=(W⊗W ^(hrtf))+(X⊗X ^(hrft))+(Y⊗Y ^(hrtf))Right=(W⊗W ^(hrtf))+(X⊗X ^(hrtf))−(Y⊗Y ^(hrtf))  Equation 3

As shown, first order horizontal-only Ambisonic decoding can beaccomplished with only six convolutions with three HRTFs.

The same optimizations can be applied to second and third orderhorizontal-only decoding. Second order requires the additional channelsU and V, and third order uses P and Q. The HRTF pair for each channelcan be computed as illustrated above for the first order using theappropriate Ambisonics coefficients as seen in Equation 4:

$\begin{matrix}{{U^{hrtf} = {\sum\limits_{k = 1}^{N}\left( {{\cos\left( {20_{k}} \right)}xS_{k}^{hrtf}} \right)}}{V^{hrtf} = {\sum\limits_{k = 1}^{N}\left( {{\sin\left( {20_{k}} \right)}{xS}_{k}^{hrtf}} \right)}}{P^{hrtf} = {{{\sum\limits_{k = 1}^{N}\left( {{\cos\left( {30_{k}} \right)}xS_{k}^{hrtf}} \right)}Q^{hrft}} = {\sum\limits_{k = 1}\left( {{\sin\left( {30_{k}} \right)}xS_{k}^{hrtf}} \right)}}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

The channels U and P share the same symmetries as the X channel; theyare symmetrical and in phase. V and Q are similar to Y as they are phaseinverted. These symmetries are taken account in the second ordercalculations for calculating the signals for each ear, shown below inEquation 5:Left=(W⊗W ^(hrtf))+(X⊗X ^(hrft))+(Y⊗Y ^(hrtf))+(U⊗U ^(hrtf))+(V⊗V^(hrft))+(P⊗P ^(hrtf))+(Q⊗Q ^(hrft))Right=(W⊗W ^(hrtf))+(X⊗X ^(hrtf))−(Y⊗Y ^(hrtf))+(U⊗U ^(hrtf))−(V⊗V^(hrft))+(P⊗P ^(hrtf))−(Q⊗Q ^(hrft))  Equation 5

Thus, second order horizontal-only Ambisonics decoding can beaccomplished with ten convolutions with five HRTFs and third order canbe accomplished with fourteen convolutions with seven HRTFs.

The present embodiment applies the optimum parameters for the mostefficient and psychoacoustically convincing binaural rendering ofAmbisonics B-format signal. The effects of the virtual loudspeakerplacement have also been considered and the following criteria have beenapplied:

i. Regular distribution of loudspeakers

ii. Maintenance of symmetry to the left and right of the listener

iii. Use of the minimum number of loudspeakers required for theAmbisonics order.

The third criterion avoids comb-filtering effects from combiningmultiple correlated signals. The relationships between the number ofloudspeakers N and the order of the system M is as set out below inequation 6:N≥2M+2  Equation 6

Thus, the present embodiments can use an “on-axis” configuration ofvirtual sounds sources. The virtual loudspeakers are located directly tothe right, left, front and back of the listener.

The above described embodiment has been given by way of example only,and the skilled reader will naturally appreciate that many variationscould be made thereto without departing from the scope of the claims.

Testing for Effect of Virtual Loudspeaker Placement and Decoding Order

The present embodiments are based on considerations of the idealplacement of the virtual loudspeakers and the ideal decoding order.Virtual Ambisonics refers to the binaural decoding of a B-format signalby convolving virtual loudspeaker feeds with HRTFs to create a binauralsignal. The testing conducted in development of the present embodimentshas been carried out to understand the best practice to render abinaural signal.

There are two possible configurations for each order, as shown in FIG. 6. On-axis loudspeaker configurations for the first order consist ofvirtual loudspeakers located directly to the right, left, front and backof the listener. The first order can have loudspeakers in this on axisconfiguration with both the ears and the nose in the first configurationand neither in a second configuration. The second order can have a pairof loudspeakers that are either on-axis with the ears or on-axis withthe nose, that is in an on-axis position the speakers are directly infront and behind the listener and in an off-axis position the speakersare directly to the right and left of the listener. The configurationapplied to the third order is shown in the bottom two configurations ofFIG. 6 . The loudspeakers are placed at 22.5 degree intervals or in 45degree intervals.

By comparing the synthesized HRTFs to measured HRTFs for each virtualloudspeaker placement, shown in FIG. 6 , the error introduced by thedecoder was compared. The loudspeaker configurations with the virtualloudspeakers directly in front and behind the listener are referred toas on-axis and those without as off-axis.

Interaural time difference (ITD) is the delay of a signal or portion ofa signal, relative to each ear. The delay is frequency dependent and theresults of testing are shown in Appendix 1 (FIG. 7A, 7B, 7C, 7D, or 7E).Lateralization cures greatly decrease above 800 Hz and phase differencesappear to have no effect above approximately 1.5 kHz. The ITD forsignals from the front of the listener is about 5 degrees or about 50μs, but these values can vary between listeners.

The ITD values were calculated from white noise convolved with the HRTFsand then filtered with ERB filters with center frequencies at 400 Hz,800 Hz, 1 kHz and 1.2 kHz.

The tests conducted were used to assess whether the multiple highlycorrelated signals would cause comb filtering. This was assessed byconsidering the error in dB over frequency for the contralateral ear andthe ipsilateral ear for the first to third order HRTF sets.

The testing for the present embodiments also considered the geometricdistances, which were used to determine how similar two objects are. Thegeometric distances were considered here to help reduce the number ofdimensions of data that need to be considered, that is, frequency,source azimuth and decoding technique. Each HRTF was considered as acollection of 64 or 512 features, depending on the length of the HRTF.The geometric distance between each HRTF can be calculated when viewingeach HRTF as an individual point in 64 or 512-dimensional space. TheEuclidean distance of two n-dimensional points P=(p1, p2, . . . , pn)and Q=(q1, q2, . . . , q4) is described below in equation 7:D(P,Q)=√{square root over ((p1−q1)²+(p2−q2)²+ . . .+(pn−pn)²))}  Equation 7

A smaller distance between two points implies that those two points aremore similar than points located further away from each other. Theclosest two points can be is if a point is located with itself. Thecosine similarity of two points measures the angle formed by the pointsinstead of the distance between them as shown in Equation 8:

$\begin{matrix}{{{Cos}\;{Sim}\;\left( {P,Q} \right)} = \frac{P \cdot Q}{{P}{Q}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

Results

Appendix 1 (FIGS. 7A, 7B, 7C, 7D, and 7E) shows the ITD for variousfrequencies;

Appendix 2 (FIGS. 8A, 8B and 8C) shows the error in dB over frequencyfor the contralateral ear; Appendix 3 (FIGS. 9A, 9B and 9C) shows theerror in dB over frequency for the ipsilateral ear Appendix 4a (FIG.10A) shows the Euclidean distance for the contralateral and theipsilateral ears for the on-axis (circles) and off-axis (triangles); andAppendix 4b (FIG. 10B) shows the Euclidean distance for thecontralateral and the ipsilateral ears for first (circles), second(triangles) and third (squares) orders.

As shown in Appendix 1 (FIGS. 7A, 7B, 7C, 7D, and 7E), for all HRTF setsthe ITD values for the first order decoding are very close to those fromthe measured HRTFs at 400 Hz and 600 Hz, for both configurations. Below800 Hz the first order decoding best mimics the cues produced by themeasured HRTF set and above 800 Hz the third order best becomes the bestat replicating the ITD values. For all frequency bands examined, thesecond order never performs better than both the first and third orders.

As shown in Appendix 2 (FIGS. 8A, 8B and 8C) and Appendix 3 (FIGS. 9A,9B and 9C), comb filtering is seen to be caused particularly at firstorder. The different HRTF sets exhibit varying error but all of the setsshow increasing error at the contralateral ear as the order increases,most noticeably at the high and low frequencies. The results shown arefor on-axis loudspeaker configurations. It was found that the error foron versus off-axis loudspeaker configurations was not significantlydifferent. However, where a difference was detected, the on-axisconfiguration was found to have less error. For example, the secondorder on-axis configurations has error ranging from −10 dB to 20 dB, butthe off-axis has error ranging from −10 dB to 30 dB.

As shown in Appendix 4 (FIGS. 10A and 10B), the Euclidean distancemeasurements have similar findings across all of the HRTF sets. For allbut the first order, the on-axis configurations produce HRTFs that arecloser in Euclidean space to the measured HRTFs than the off-axisconfigurations for both the ipsilateral and contralateral ears. Appendix4a—FIG. 10A shows the Euclidean distance for the first order decodingfor both on-axis and off-axis configurations. The on-axis configurations(shown with circular markers) are consistently less than the off-axis(shown with triangular markers) for the contralateral ear while theipsilateral ear has a preference for the on-axis configuration only inthe front plane. As it is known that humans localize sounds sources tothe front better than to the rear, we consider that the on-axisconfiguration is closest overall to the measured HRTFs.

All four of the HRTF sets show a considerable increase in Euclideandistance from the measured HRTFs as the order increases, as shown inAppendix 4b—FIG. 10B. This is true for both the contralateral andipsilateral ears. The ipsilateral ear signals tended to have slightlyhigher distances than the corresponding contralateral signal.

The cosine similarity testing did not provide as clear an indicator asthe Euclidean distance testing. The on-axis configuration is marginallybetter than the off-axis for both orders, but was found to be highlydependent on the HRTF set. When considering the increasing order withsimilar loudspeaker configurations, it was found that the second orderprovides the closest results to the measured HRTFs for the ipsilateralear, but the first order is consistently better for the contralateralear.

CONCLUSIONS

It was found that there was evidence to suggest that the bestconfiguration for virtual loudspeaker arrangement for the binauralrendering of horizontal-only Ambisonics was an on axis configuration.For all HRTF sets the most accurately synthesized sets were found to bethose decoded at first order.

The cosine similarity results and the increased frequency error of thecontralateral ear signals confirms that for Ambisonics a signal isconstantly fed to all loudspeakers regardless of the location of thevirtual source. This is shown in the measured HRTFs when thecontralateral ear received the least amount of signal when the soundssource is completely shadowed by the head; this is in contrast to theAmbisonics signal where the contralateral ear will still receive asignificant amount of signal.

The ITD measurements taken in these test use a psychoacoustical model topredict what a listener would perceive. ITD values below 800 Hz forfirst order decoding have excellent results consistently across all HRTFsets, especially for on-axis configurations. Second and third orderdecoding does not perform as well below 800 Hz. Third order was found toperform well above 800 Hz but not to the same accuracy that is seen infirst order decoding at the lower frequency bands. ITD cues become lesspsychoacoustically important as frequency increases so we conclude thatfirst order decoding may most accurately reproduce psychoacoustic cues.

For first and second order decoding, the on-axis configurations performbetter, both in terms of the geometric distances and the frequencyerror. We have extrapolated that for third axis the on-axis loudspeakerconfiguration would also be the optimum set-up.

We have also found that the Ambisonics encoding and decoding order doesnot necessarily increase the spatialization accuracy. First orderdecoding accurately reproduces the ITD cues of the original HRTFs setsat lower frequencies. Higher order encoding and decoding tend toincrease the error at the contralateral ear.

What is claimed is:
 1. A method comprising: generating audio outputs associated with a plurality of audio recordings by decoding channel signals determined using a square root of a head-related transfer function and a number of speakers in a speaker system; and activating a navigation feature to change a number of the audio outputs concurrently playing through the speaker system.
 2. The method of claim 1, further comprising enabling selection of an audio output.
 3. The method of claim 1, wherein the navigation feature is configured to change a location of an audio output in the speaker system.
 4. The method of claim 1, further comprising: determining an online music store associated with one of the audio outputs.
 5. The method of claim 1, wherein angular relations between the audio outputs are maintained during navigation using the navigation feature.
 6. The method of claim 1, wherein the navigation feature comprises tracking motion of a user.
 7. The method of claim 1, wherein the audio outputs are generated according to a musical preference associated with a user.
 8. The method of claim 1, wherein the method is performed in a mobile device.
 9. A system comprising: a user interface; and a processor in communication with the user interface and configured to: generate audio outputs associated with recordings based on channel signals determined using a square root of a head-related transfer function and a number of speakers in a speaker system; and activate a navigation feature to change a number of audio outputs concurrently playing in a three-dimensional listening area associated with an entity.
 10. The system of claim 9, wherein the processor is further configured to store map data representative of one or more similarity maps.
 11. The system of claim 9, wherein the processor is further configured to enable selection of a defined number of audio outputs.
 12. The system of claim 9, further comprising an accelerometer.
 13. The system of claim 9, wherein the user interface comprises tangible input controls.
 14. The system of claim 9, wherein the speakers are arranged in an on-axis configuration.
 15. The system of claim 9, wherein the processor is further configured to display a three-dimensional listening area.
 16. A non-transitory computer-readable medium having instructions stored thereon, the instructions comprising: instructions to generate audio outputs associated with recordings by decoding channel signals determined using a square root of a head-related transfer function and a number of speakers in a group of speakers of a sound system; and instructions to activate a zoom feature to modify a number of the audio outputs concurrently playing in a three-dimensional listening area surrounding an entity.
 17. The non-transitory computer-readable medium of claim 16, wherein the instructions further comprise: instructions to arrange the audio outputs according to properties associated with the recordings.
 18. The non-transitory computer-readable medium of claim 16, wherein the instructions further comprise: instructions to move the entity within the three-dimensional listening area, wherein the audio outputs are stationary.
 19. The non-transitory computer-readable medium of claim 16, wherein the three-dimensional listening area comprises a type of listening environment, and wherein the instructions further comprise: instructions to change the type of listening environment.
 20. The non-transitory computer-readable medium of claim 19, wherein the type of listening environment comprises a living-room type or a religious venue type. 